The present invention relates to a method for obtaining metallic alloys composed of a combination of several metallic elements, to be used in dentistry.
A great number of alloys for dental applications are in commun use; they are composed of different combinations of the most used elements for such applications, such as gold, platinum, palladium, silver and copper with the addition of a certain number of other elements introduced therein in order to comply with specific requirements or to fulfil peculiar functions.
The alloys normally used, owing to the lack of data concerning their properties, are essentially of empirical origin, the studying and producing of the same being almost exclusively based on the fundamental principles and essential features of its composing elements and on the experimental results of tests.
The formulating of a satisfactory general theory concerning the metallic alloys has not yet reached its achievement and still requires much work based on the experimental and theoretical data in order to define and understand the numerous factors influencing the structure of the alloy-forming phases and the complexity of the interactions which the different elements exert on each other.
The main factors concerning the solid-state solubility between several elements can be summarized as follows:
size of atoms; a favourable condition is that of a maximum difference in sizes of 15%;
type of crystal lattice; only the elements having the same crystal lattice allow the formation of complete series of substitution solid solutions;
the same valence; metals having the same valence are more suitable to form substitution solid solutions.
Keeping in mind these factors and the fact that if a metal should have a perfectly regular crystal structure, that is to say devoid of simple or multiple vacancies or dislocations, it could exhibit quite superior qualities with respect to those found in reality, it appears necessary, when forming alloys, to achieve the best distribution and uniformity of the elements in the crystal lattice; on the contrary, it is usually possible to notice an almost causal distribution of the solute atoms in the solvent lattice and, as a result, the presence of vacancies and dislocations.
The atoms of the elements in use respect the above mentioned characteristics required for the formation of substitution solid solutions, as well as the physico-chemical properties suitable for dental applications but the alloys actually in use, owing to their empirical formulas, do only casually possess all the necessary mechanical and electro-chemical features which can only be obtained by forming a perfectly uniform and balanced lattice.